Friction welding is a process by which metals, and/or other materials, are joined by heat, which is generated when the parts are rubbed together under high pressure. The advantages of friction welding include very rapid completion rates, good mechanical properties, and the elimination of the need for shielding gases under most circumstances. There are at least twenty variants of friction welding processes. Some of those variants include rotary friction welding, friction stud welding, radial friction welding, linear friction welding, orbital friction welding, third-body friction welding, and friction taper plug welding.
Friction stir welding is a relatively new friction welding process. It involves rotating a small tool between two closely butted components. Frictional heating causes the materials in the components to soften and the forward motion of the tool forces material from the front of the tool to the back, where it consolidates to form a solid-state weld. Stir welding processes thus combine the flexibility of mechanized arc welding with the desirable results of friction welding.
One particular benefit of friction stir welding is that the formation of the weld or joint is autogenous and is created by the solidification of plasticized parent materials rather than a filler material, as is commonly used in conventional welding processes. In addition, the friction stir weld joint includes a nugget having a refined grain structure with grains having an equiaxed shape and grain sizes ranging from approximately 0.0001 to 0.0002 inches (approximately 3 to 5 microns). As a result of the improved grain structure, the friction stir weld joint resists formation and propagation of micro-cracks and exhibits improved strength, ductility, toughness, and improved corrosion and fatigue resistance.
During a friction stir welding process, load cells inherent to the system must be tested off-line periodically to verify their accuracy. These tests usually check stir welding loads one axis at a time in either axial or radial load directions. The load cells on the machine are then recalibrated to meet the calibrated cells. This can be very time consuming, and results do not necessarily correlate to the anticipated loads of a particular welding process program.
Thus, there is a need for improved methods and apparatus for friction stir welding and, in particular, for stir welding load confirmation.
The disadvantages associated with current load confirmation tools have made it apparent that a new technique for stir welding confirmation is needed. The new technique should verify path and anticipated program loads before an actual friction stir welding tool is embedded in a material undergoing welding or joining.